Increasingly, in an era when truffles are farmed and Whole Foods sells fresh porcini, the ingredients that chefs seek are not the ones anyone can order; they’re the ones that few have ever heard of. They are the most unusual, not the most expensive. And even if they’re plentiful, they’re exclusive: you need either to know where to go and what to gather, or who to call....

The professional kitchen isn’t known as a sentimental place, but foraging seems to stir these kinds of passionate feelings. “It taps into something emotional — you’re nourished by the place where you live,” Mr. Patterson said. “Trends come and go. This is different.”